12 - Alkanes Flashcards
Are alkanes saturated or unsaturated?
Saturated
Physical Properties of alkanes
- polarity
- boiling points
- solubility
- reactivity
Polarity
Alkanes are almost non polar because the electronegativities of carbon and hydrogen are similar
The intermolecular forces between their molecules are weak van dear Waals forces
The larger the molecule, the larger the vdW force
Solubility of alkanes
Insoluble in water
Water molecules are held together by hydrogen bonds which are much stronger than the vdW forces that act between alkane molecules,
Boiling points of alkanes
As the length of the alkane chain increases, so does the boiling point. This is because the intermolecular forces increase meaning more energy is required to break the bonds.
Reactivity of alkanes
Alkanes are relatively unreal it. They have strong carbon-carbon and carbon-hydrogen bonds
They don’t react with: acids, bases, oxidising agents or reducing agents.
However, they burn and react with halogens
Products of complete combustion
Carbon dioxide + Water
Products of incomplete combustion
Carbon/Carbon monoxide + water
When to know if carbon monoxide or carbon is produces
Carbon monoxide: a poisonous gas is produces
Carbon: black product (soot)
What are alkanes used as
Fuels
Why are alkanes good fuels
Combustion reactions give out heat and have negative enthalpy changes. Which means lots of heat is given out basically so it is a good fuel
Different pollutants produced as a results of burning alkanes
Carbon monoxide
Nitrogen oxides
Sulfur dioxide
Carbon particulates
Unburnt hydrocarbons
Carbon dioxide
Water vapour
Why is carbon monoxide a pollutant
Poisonous gas
Why are nitrogen oxides a pollutant
Oxides react with water vapour and oxygen in the air to form nitric acid —> acid rain
How are nitrogen oxides produced?
Under extreme heat and pressure
N2 + O2 -> 2NO
How is Sulfur dioxide produced?
Produced from Sulfur containing impurities present in crude oil